The invention relates to a main girder of a crane for a crane trolley moving in a horizontal direction along the girder, the main girder comprising a cellular structure in a longitudinal direction thereof that has at least two separate, yet interconnected, longitudinal cellular elements. On the top or bottom surface of the main girder in question there is or will be mounted as least one travel rail structure in a longitudinal direction of the main girder for the trolley.
Prior art main girders are typically beams that are made of relatively thick steel plates by welding or casing structures and have an upper plate, lower plate and one or more web plates between them. The travel rail structure is then preferably placed above the web plate so that local load caused by the trolley would be transferred to the web plate/plates.
To avoid web plate stability from being lost, the thickness of the plates used in the structure is increased and/or transverse and/or longitudinal reinforcements are added to the web until sufficient certainty against stability loss is obtained.
In these conventional solutions the number of parts is high and plenty of welding seams are used. The structure restricts minimizing of web plate thicknesses because then the number of reinforcements will be high. In some cases a conventional structure sets limits to utilization of strong steels.